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Introduction:
Operational Technology (OT) and Industrial Control Systems (ICS) increasingly rely on Windows-based machines for data historians, engineering workstations, and HMIs. However, extending your corporate IT Active Directory (AD) into OT environments creates a direct attack pathway that adversaries actively exploit to cause physical damage, production outages, and safety failures.
Learning Objectives:
- Identify the technical risks of AD trust relationships between IT and OT forests
- Implement completely separate AD forests for OT with no trusts or cross-authentication
- Use PowerShell, netdom, and firewall rules to audit and enforce network segmentation between IT and OT domains
You Should Know:
- The Hidden Danger of Active Directory Trusts in OT
Many engineers mistakenly believe that adding a one-way trust between IT AD and OT AD is safe. In reality, any trust—even selective authentication—leaks Kerberos ticket-granting tickets, SID history, and NTLM hashes across boundaries. Attackers who compromise a low-privilege IT account can pivot to OT by requesting service tickets for OT resources.
Step‑by‑step guide to detect existing AD trusts (run on a domain controller or management workstation):
Windows (PowerShell as Admin):
List all trusts for the current domain
Get-ADTrust -Filter | Format-Table Name, TrustDirection, TrustType, IsTreeParent
Check for outgoing or incoming trusts to OT domains
Get-ADTrust -Filter {TargetName -like "OT" -or TargetName -like "ICS"}
Using netdom (Command Prompt):
netdom trust <IT-Domain-Name> /domain:<OT-Domain-Name> /verify netdom trust <OT-Domain-Name> /domain:<IT-Domain-Name> /verify
Linux (from a jump host that can query AD via LDAP):
Install ldap-utils, then enumerate trust relationships ldapsearch -x -H ldap://it-dc.corp.com -b "CN=System,DC=corp,DC=com" "(&(objectClass=trustedDomain))" name trustDirection
If any trust is found, remove it immediately using `Remove-ADTrust` or netdom trust /remove.
2. Building a Standalone OT AD Forest: Step‑by‑Step
A separate OT forest must be physically or virtually isolated, with its own DNS, root CA, and no network route to IT domain controllers. Do not reuse the same forest root domain name.
Step‑by‑step deployment for a new OT forest:
- Provision an isolated Windows Server (2022 or 2019) on OT network segment.
- Assign static IP and DNS pointing to itself (127.0.0.1 initially).
3. Install AD DS role via PowerShell:
Install-WindowsFeature -Name AD-Domain-Services -IncludeManagementTools
4. Promote to new forest (not a child domain or tree):
$securePass = ConvertTo-SecureString "YourOTComplexPassword123!" -AsPlainText -Force Install-ADDSForest -DomainName "ot-ics.local" ` -SafeModeAdministratorPassword $securePass ` -Force -NoRebootOnCompletion
5. Reboot and verify no DNS forwarders point to IT DNS servers.
6. Configure Windows Firewall on all OT domain members to block all inbound/outbound traffic to IT subnets (see Section 4).
Critical: Never install Microsoft Entra Connect (Azure AD Connect) or any identity sync tool between the forests.
3. Hardening OT Windows Systems Without IT AD
When OT Windows machines are removed from IT AD, they lose centralized Group Policy management. Use local policy, PowerShell Desired State Configuration (DSC), or a separate OT management system.
Apply security baseline by script (run locally on OT workstation):
Disable NTLMv1, force SMB signing, block guest logons Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa" -Name "LmCompatibilityLevel" -Value 5 Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters" -Name "RequireSecuritySignature" -Value 1 Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager" -Name "ProtectionMode" -Value 1 Audit local user logins (no domain fallback) auditpol /set /subcategory:"Logon/Logoff" /failure:enable /success:enable
Linux command to remotely verify hardening (if OT segment has a Linux admin host):
Use nmap to check for open AD ports (should be closed on OT edge) nmap -p 88,389,445,464,636,3268-3269 -Pn --open <OT-Workstation-IP> Use enum4linux to test for null session from IT side (should fail) enum4linux -a <OT-DC-IP> 2>&1 | grep -i "session setup failed"
- Firewall Rules to Block All AD Communication Between IT and OT
Network segmentation is the second layer. Even if an OT DC is compromised, no routing to IT should exist. Use Windows Firewall on OT domain members to enforce egress filtering.
Windows Firewall (PowerShell as Admin) – block outbound to IT subnet:
$ITSubnet = "192.168.0.0/16" Replace with actual IT subnet
$ADPorts = @(53,88,135,139,389,445,464,636,3268,3269,5985,5986,9389)
foreach ($port in $ADPorts) {
New-NetFirewallRule -DisplayName "Block AD port $port to IT" `
-Direction Outbound -Protocol TCP -LocalPort $port `
-RemoteAddress $ITSubnet -Action Block
}
Linux iptables (on OT-IT gateway or jump host):
Drop all traffic from OT network (10.0.0.0/24) to IT network (192.168.0.0/16) on AD ports iptables -A FORWARD -s 10.0.0.0/24 -d 192.168.0.0/16 -p tcp -m multiport --dports 88,389,445,464,636,3268,3269 -j DROP iptables -A FORWARD -d 10.0.0.0/24 -s 192.168.0.0/16 -p tcp -m multiport --sports 88,389,445,464,636,3268,3269 -j DROP
5. Verifying Separation with Automated Auditing
Run regular checks to confirm no accidental bridges exist. Use PowerShell remoting from a secured OT management host.
Audit script to verify no AD cross-authentication:
Test if an OT machine can resolve IT domain
if (Resolve-DnsName "it.corp.com" -ErrorAction SilentlyContinue) { Write-Warning "DNS leak detected!" }
Attempt a test authentication from OT to IT (should fail)
$cred = Get-Credential "IT\testuser"
try { Test-ComputerSecureChannel -Server "IT-DC.it.corp.com" -Credential $cred -ErrorAction Stop }
catch { Write-Host "Properly blocked: $_" }
Linux cron job for continuous monitoring on OT network:
Check for unauthorized LDAP queries to IT every 5 minutes /5 tcpdump -i eth0 -n -c 10 'dst host 192.168.0.10 and (tcp port 389 or udp port 389)' >> /var/log/ot-it-ldap.log
- Moving OT Windows to Local Accounts and Credential Guard
Without AD, each OT workstation/server should use unique local administrator passwords managed via a vault (e.g., LAPS for workgroup). Enable Windows Defender Credential Guard to prevent pass-the-hash attacks.
Enable Credential Guard (requires Hyper-V):
On Windows 10/11/Server 2016+
$isEnabled = (Get-DeviceGuard -All).CredentialGuard
if (-not $isEnabled) {
$path = "HKLM:\SYSTEM\CurrentControlSet\Control\DeviceGuard"
New-ItemProperty -Path $path -Name "EnableVirtualizationBasedSecurity" -Value 1 -PropertyType DWORD -Force
New-ItemProperty -Path $path -Name "RequirePlatformSecurityFeatures" -Value 1 -PropertyType DWORD -Force
New-ItemProperty -Path "$path\Scenarios\CredentialGuard" -Name "Enabled" -Value 1 -PropertyType DWORD -Force
Write-Host "Reboot required"
}
What Undercode Say:
- Key Takeaway 1: Any AD trust between IT and OT is a critical vulnerability – treat OT as a hostile network and enforce complete forest isolation.
- Key Takeaway 2: Defense requires both logical (separate forests, no trust) and physical/network (firewall blocks, no routing) controls, verified by automated audits.
Analysis: The post by Mike Holcomb reflects a truth that incident responders see repeatedly – attackers use AD misconfigurations to move from a phishing email to a turbine shutdown in hours. IT security teams often undervalue OT risk because they rarely deal with safety consequences. However, modern OT environments are not air-gapped; they share Ethernet, patching infrastructures, and even help desk staff. The only safe assumption is that IT will be compromised. By maintaining separate AD forests with no trusts, you force an attacker to re‑exploit the OT side from scratch – a massive increase in operational friction. Tools like netdom, Get-ADTrust, and firewall rules are free, but the discipline to enforce them is priceless. Remember that a “temporary” trust for patching or user sync becomes permanent – just don’t do it.
Prediction:
As OT/ICS environments adopt more Windows-based edge devices and cloud management planes, we will see threat actors increasingly target identity federation misconfigurations to jump from IT to OT. Regulations such as NERC CIP and IEC 62443 will soon mandate explicit separation of authentication directories, driving demand for OT‑specific identity solutions (e.g., Rockwell Automation’s FactoryTalk with local authentication). Organizations that continue to bridge AD forests will suffer publicly disclosed safety incidents within the next 18 months, leading to insurance exclusions for hybrid AD deployments. The future is not integration – it is hardened, isolated, and audited separation.
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Reported By: Mikeholcomb Connecting – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
